The present invention relates to a method and device for detecting a disruption of a positioning measurement differential correction message of a satellite geolocation device.
The invention falls within the field of securing satellite geolocation, in the context of possible intentional disruptions seeking to deceive a geolocation device.
It is applicable in many fields, for example aeronautics, maritime transport, road guidance, vehicle and robot guidance.
Today, satellite geolocation is widely used for precise positioning or for moving vehicles, provided with geolocation devices.
Owing to GNSS (Global Navigation Satellite System), a geolocation device, including a receiver for signals emitted by an appropriate satellite, is able to receive navigation messages including radio signals emitted by a plurality of satellites and to provide, after computation, positioning information of the carrier of the geolocation device in a geographical reference.
Each geolocation device captures information sent in radio signals transmitted by various satellites, and computes, for each satellite in view and from that received information, a positioning measurement, which is an estimate of the distance between the geolocation device itself and the satellite in view, which is also called pseudo-range. The pseudo-range is different from the actual distance between the satellite in question and the geolocation device due to potential errors in the received information, for example due to atmospheric conditions in the troposphere, and the error in the internal clock geolocation device. It is possible to compute a positioning measurement error correction from information sent by a plurality of separate satellites.
The GPS system (Global Positioning System) is a widely used satellite geolocation system.
Known systems exist for increasing satellite geolocation precision.
For example, the geostationary satellite spatial augmentation system, called SBAS (satellite-based augmentation system), uses geostationary satellites that listen to the constellation of positioning satellites of the GNSS system, such as the GPS system, and is able to send a receiving geolocation device correction messages comprising correction information for positioning measurements and integrity relative to each of the positioning satellites.
The SBAS system accounts for errors from separate sources: ionospheric error, tropospheric error. It includes orbit corrections for GNSS satellites, and specific corrections. The SBAS system also provides integrity information, designed to quantify the confidence associated with the sent correction information.
Technical standard RTCA DO-229D “Minimum Operational Performance Standards for Global Positioning System/Wide Area Augmentation System Airborne Equipment” defines the SBAS spatial augmentation system relative to the GPS system.
One such alternative augmentation system for positioning precision is the GBAS system (ground-based augmentation system), which uses reference segments positioned on the ground, these reference segments including GNSS receivers able to receive information from positioning satellites and compute their position from that received information. The precise position of the reference segments being known, it is possible to compute positioning measurement corrections. The GBAS system also provides integrity information, similarly to the SBAS system.
Geolocation security and integrity verification systems exist aiming to detect the presence of added disruption signals, also called decoy signals, similar to the radio signals emitted by the satellites but bearing erroneous information seeking to cause an erroneous computation of positioning information.
However, it is also necessary to consider the possibility of intentional disruption of differential correction messages for positioning measurements used by the SBAS or
GBAS receivers, seeking to cause an erroneous position to be computed for the geolocation device including the receiver.
The invention aims to detect such disruptions of positioning measurement differential correction messages emitted by satellite geolocation precision augmentation systems.